Ohlins Spring Rate Calculator
Professional Suspension Tuning & Setup Tool
Calculate Your Ideal Spring Rate
Enter your rider and motorcycle details to determine the recommended Ohlins spring rate (N/mm) required to achieve proper race sag.
95 N/mm
Metric Rate
Est. Rear Load
Est. Ohlins Series
Sag Sensitivity Analysis
How changes in rider weight affect sag with the recommended spring:
Weight vs. Spring Rate Reference
| Rider Weight (kg) | Recommended Rate (N/mm) | Est. Preload Required |
|---|
*Table assumes constant leverage ratio and bike weight.
What is an Ohlins Spring Rate Calculator?
An Ohlins spring rate calculator is a critical tool for motorcycle suspension tuning, designed to help riders determine the correct stiffness (spring rate) for their rear shock or front forks. Getting the correct spring rate is the foundation of motorcycle handling; no amount of damping adjustment (clickers) can compensate for a spring that is too soft or too stiff for the combined weight of the rider and the machine.
Ohlins, a leader in advanced suspension technology, typically denotes their spring rates in Newtons per millimeter (N/mm). However, many riders are familiar with kg/mm or lbs/in. This calculator bridges that gap by computing the ideal rate based on physics and converting it into standard Ohlins formats.
Riders of all disciplines—from MotoGP track days to motocross and adventure touring—use an Ohlins spring rate calculator to ensure their suspension operates in the “sweet spot” of its travel, maximizing traction, comfort, and safety.
Ohlins Spring Rate Formula and Mathematical Explanation
Calculating the correct spring rate involves analyzing the load placed on the suspension and the mechanical advantage (leverage) the swingarm has over the shock. The core formula used in this calculator is derived from Hooke’s Law and suspension kinematics:
K_spring = (Load_rear / Sag_target) × (Leverage_Ratio)²
Variables Explained
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Load_rear | Total mass supported by the rear wheel | kg | 150 – 400 kg |
| Sag_target | Desired compression from full extension | mm | 25 – 105 mm |
| Leverage_Ratio | Ratio of wheel travel to shock stroke | Ratio : 1 | 1.0 (PDS) – 3.0 (Linkage) |
| K_spring | Stiffness of the spring | N/mm | 60 – 160 N/mm |
The squared term for the Leverage Ratio is crucial. Since the shock moves less than the wheel, the spring must be exponentially stiffer to support the same load at the wheel.
Practical Examples: Tuning for Different Disciplines
Example 1: The Track Day Rider
Scenario: A rider on a Yamaha R1 (Linkage ~2.0) weighs 85kg in full leathers. The bike is 200kg wet. They want a firm “Race Sag” of 30mm.
- Total Rear Load: Approx 190kg (assuming bias).
- Target Sag: 30mm.
- Calculation: The calculator determines a rate near 95 N/mm. This stiff spring prevents the rear from squatting too much under hard acceleration out of corners.
Example 2: The Adventure Tourer
Scenario: A rider on a BMW GS with luggage weighs 110kg. The bike is heavy (240kg). They need comfort and compliance, aiming for 45mm sag.
- Total Rear Load: Approx 230kg.
- Calculation: Despite the heavier load, the softer sag target and different leverage ratio might suggest a spring rate of 140 N/mm (Ohlins equivalent) to handle the immense weight without bottoming out.
How to Use This Ohlins Spring Rate Calculator
- Input Rider Weight: Enter your weight wearing all your riding gear. A helmet and leathers can add 10-15kg!
- Input Bike Details: Enter the wet weight of your motorcycle.
- Determine Leverage Ratio:
- If your shock attaches directly to the swingarm (e.g., KTM PDS), use ~1.0 – 1.2.
- If you have a linkage system (e.g., Japanese sportbikes), use ~1.8 – 2.5. Consult your service manual for exact stroke/travel data to calculate: Wheel Travel ÷ Shock Stroke.
- Set Desired Sag:
- Sport/Track: 25-30mm
- Street: 30-40mm
- Off-Road: 95-105mm
- Review Results: The calculator provides the rate in N/mm (Ohlins standard) and kg/mm.
Key Factors That Affect Ohlins Spring Rate Results
Several variables can influence the final spring choice beyond just weight:
- Linkage Progression: Some linkages start soft and get stiffer (progressive). A standard calculator assumes a linear average, so you might need to adjust slightly based on the curve.
- Preload Adjustability: If you often carry a passenger, choose a spring for your solo weight but ensure you have a hydraulic preload adjuster to add tension when loaded.
- Friction (Stiction): Old linkage bearings can create drag, making a spring feel stiffer than it is. Ensure your suspension moves freely before measuring sag.
- Unsprung Weight: Heavier wheels or swingarms affect how the suspension reacts, though this primarily influences damping rather than spring rate.
- Riding Style: Aggressive riders who brake late and accelerate hard often prefer slightly stiffer springs than the calculator suggests to maintain geometry stability.
- Aerodynamic Load: At very high speeds (150mph+), downforce can compress suspension. Dedicated race teams factor this into their spring rate calculations.
Frequently Asked Questions (FAQ)
Newtons (N) is the standard SI unit for force. Ohlins, being a European engineering company, adheres to SI standards. 1 kg/mm is approximately 9.807 N/mm.
No. A spring supports weight; the shock (damper) controls energy. A stiff spring on a blown shock will result in a dangerous “pogo stick” effect.
The default of 2.0 is a generic average for linkage bikes. For precision, measure your wheel travel and shock stroke, or check your bike’s specific manual.
Ohlins springs usually come in 5 N/mm or 10 N/mm increments. Generally, round up for track use (stability) and round down for street use (comfort).
The physics are similar, but the leverage ratio on forks is almost always 1:1. Set the leverage ratio to 1.0 to estimate fork spring rates.
The “Rear Weight Distribution” input handles this. Sitting further back increases rear load. If you sit neutrally, the standard distribution applies.
Free sag is how much the bike settles under its own weight without a rider. If you get correct rider sag but have no free sag (0mm), your spring is too soft and you have too much preload.
Yes. The “Wet Weight” of the bike includes fuel, oil, and coolant. A full tank can add 15-20kg, significantly affecting the sprung mass.
Related Tools and Internal Resources
Explore more tools to perfect your motorcycle setup:
- Motorcycle Gear Ratio Calculator – Optimize your sprockets for acceleration or top speed.
- Static Sag vs Rider Sag Guide – A deep dive into measuring your baseline suspension numbers.
- Fork Oil Viscosity Chart – Choose the right damping fluid for your new springs.
- Track Day Tire Pressure Tool – Calculate ideal pressures based on track temperature.
- Chain Length Calculator – Determine link count when changing gearing.
- Power to Weight Ratio Calculator – See how dropping weight affects performance.